We previously observed that muscle blood flow (MBF) is primarily directed to the active oxidative muscle fibers within muscles of rats during treadmill exercise. Since muscle fiber recruitment patterns and the relative level of activities of muscles are distinctly different in swimming and treadmill exercise, we hypothesized that the distribution of MBF would also be different. The purpose of this study was to measure the distribution of MBF in swimming rats for comparison with the patterns previously observed in treadmill exercise. MBF was measured with labeled microspheres in 25 hindlimb muscles before, during, and after 5 min of swimming. During swimming, MBFs ranged from 10 to 403 ml X min-1 X 100 g-1 in the white vastus lateralis and red tibialis anterior, respectively. MBFs were increased during swimming in most muscles with the flexor muscles generally showing larger increases than the extensor muscles. Comparison of swimming with treadmill exercise indicates that swimming produces greater increases in MBFs in flexor muscles than in extensor muscles, whereas treadmill exercise produces larger increases in extensor muscles. The increased MBF during swimming was directed to the fast-twitch oxidative fibers. Therefore regional hindlimb MBF distribution is different in swimming than in treadmill exercise, and it appears that MBF is matched to the fiber recruitment patterns during both types of locomotory exercise.